Influencing sedimentation

ABSTRACT

This invention relates to artificial seaweed arrays for influencing the sedimentation and movement of solid particles of material in seas, lakes and other bodies of water and in particular to a more easily laid unified array structure and a method for laying it.

United States Patent 1 1 v Rhodes et a1.

[111 3,745,771 [4 1 Jul 17, 1973 INFLUENCING SEDIMENTATION [75] Inventors: Paul Cephas Rhodes, Harrogate;

Stanley Temple Cope, Horse Heath, both of England [73] Assignee: Imperial Chemical Industries Limited, London, England 221 Filed: Jan. 4, 1971 211 Appl. No.: 103,419

30 Foreign Application Priority Data Feb. 25, 1970 Great Britain 9,114/70 [52] 11.8. C1. 61/38, 61/3 [51] Int. Cl. E02b 3/12 [58] Field of Search 61/3, 4, 5 6, 37, 61/38 [56] References Cited UNITED STATES PATENT 3,299,640 '1/1967 Nielsen ..61/3

3,517,514 6/1970 3,590,585 6/1971 DcWinter ..6l/3

Frerichs et a1 .1 (11/38 FOREIGN PATENTS O11 APPLICATIONS 1,164,842 9/ 1969 Great Britain Primary ExaminerDavid J. Williamowsky 1 Assistant Examiner-Philip C. Kann'an AttorneyCushman, Darby & Cushman [57] ABSTRACT This invention relates to artificial seaweed arrays for influencing the sedimentation and movement of solid particles of material in seas, lakes and other bodies of water and in particular to a more easily laid unified array structure and a method for laying it.

11 Claims, 3 Drawing Figures PAH-mum 1 11913 Inventors P00 Cap/was- P190055 8744/45) lav/=3: C'OPE Q A ltorneys INFLUENCING SEDIMENTATION United Kingdom patent specification No. 984,077 describes artificial seaweed arrays comprising a plurality of ropes or chains, laid parallel to each other and secured to anchors at the ends, having tufts of buoyant threads, tapes or filaments attached at intervals along their lengths and the use of these arrays in controlling the migration of material at coasts and shores. Such arrays are generally cheaper and more effective in, for example, protection of coasts against erosion, than concrete or wooden groynes which have frequently been used hitherto.

According to the present invention we provide an artificial seaweed array comprising strand material such as a plurality of tufts or loops of threads, tapes or filaments attached to a reticular base structure, the loops having apex portions floating freely in the water.

Also according to this invention we provide a method for influencing the sedimentation and movement of solid particles of material in seas, lakes and other bodies of water wherein an array of artificial seaweed comprising a plurality of tufts or loops of threads, tapes or filaments attached to a reticular base structure is placed at the bottom of a body of water and secured by anchoring means.

The material comprising the tufts or loops of an array according to this invention may be self-buoyant, that is to say of low water absorptivity and of specific gravity less than that of water into which an array is laid. In this case the reticular structure is laid on the bottom of a body of water with the attached tufts or loops disposed on the upper side to form an upward extending floating mass when immersed in water. Alternatively the tuft or loop material may be denser than water and the reticular base lighter in which case an array is laid with the reticular base uppermost and in the water the tufts or .loops will depend from it. Alternative to supporting the depending tufts or loops by a buoyant reticular base the base and tufts or loops may be wholly supported by independent buoyant means or rigid supports extending from the bottom of a body of water.

Preferred materials for the tufts or loops of an array are synthetic polymeric materials either those which are inherently of low density, as for example polyethylene or polypropylene or those of higher density, as for example polyesters and polyamides which may if necessary be converted to a low density form by enclosing air or other gas within the material, as for example by incorporating a blowing agent which by decomposition during the shaping into tapes or filaments produces a cellular product.

A base structure to which tufts or loops are attached to provide an array according to this invention is'of openwork form and may resemble a net or woven structure having large apertures or meshes. A base structure is preferably of sufficient stiffness to remain substantially flat when being handled and laid and rigid stiffeners may be incorporated at intervals in a lateral ample a two-dimensional series of squares or diamonds and joining the strands at cross-over points. Joining may be effected by binding, welding or glueing, by means of clips or if sufficiently flexible by knotting as in net manufacture. Joining of the crossover points of a base structure may be combined with attachment of tufts or loops particularly if binding, clipping or knotting methods are used. In this way a unified array is produced, somewhat resembling a carpet, which may be very conveniently handled in long lengths of various widths by winding on a suitable beam or drum.

This ease of handling also greatly facilitates the laying of an array in a body of water. One convenient way to do this is to wind a length of the prepared array structure on a beam and to mount this upon a boat or barge, to secure a leading end of the array at the bottom of a body of water and then by moving the boat or barge in the required direction and controlling the rate of unwinding of the beam an array may be continuously laid in the width of a beam. Wider arrays may be laid in the same fashion by mounting more than one beam on the boat or barge or by successive runs of the boat or barge. Alternative to mounting a beam on a boat or barge a beam or a plurality of beams may be made so as to float and be towed behind a boat or barge to effect the laying of an array.

Anchoring means if sufficiently compact may be attached at intervals to an array either as wound on a beam or as the array unwinds in the laying operation. This is the preferred method of anchoring an array and it is further preferred to use anchoring means which do not require to be dragged across the sea bed to become embedded but which may be firmly positioned at the point of contact with the sea bed. Such anchoring means is described in copending patent application No. 7791/70. Conventional swinging fluke or admiralty pattern anchors may be used in the initial securing of a leading end of an array to the sea bed and may also be used for securing the array along its length if means to draw the array tight at the position of anchor embedding can be provided.

The invention is illustrated by way of example in the attached drawings wherein:

FIG. 1 is a perspective view of part of an array wherein a loop form of artificial seaweed is shown;

FIG. 2 is an enlarged partial cross-section of a cross over point of a reticular base structure whereat a portion of an artificial seaweed loop is also attached and FIG. 3 is a plan view of one method of laying an array according to this invention.

In these drawings like numerals refer to like parts.

Referring to FIG. I a reticular base structure is made up of longitudinal members 1 and transverse members 2 at the cross-over points of which continuous lengths of bundles of threads, tapes or filaments 3 are attached with sufficient material in a segment between points of attachment to form a loop. One manner of attachment is shown in more detail in FIG. 2 wherein a transverse member 2 is knotted around a longitudinal member I, a portion of a length of artificial seaweed 3 is taken around the joined parts 1 and 2 and bound in place at the cross-over point by means not shown. The material of the lengths 3 may be self-buoyant or non-buoyant and the reticular base structure is laid above or below the loops of artificial seaweed accordingly. FIG. 3 illustrates one method of laying an array attached to a reticular structure.

on a drum 5 which is carried on an axle (not shown).

mounted in a frame 6. The whole drum, array and frame float in water and are attached by lines 7 to a towing vessel 8. In laying an array an anchor 9 is attached to the outermost two longitudinal members 1 and a sufficient length of the array is unwound from the drum 5 to allow the anchor 9 to be accurately positioned. Towing vessel 8 then proceeds away from the anchor 9 and is restrained in the required line of movement by two lines10 at the bow the ends of which have been anchored firmly in position before laying starts. Laying is then completed by paying out the array by controlled rotation of the drum 5 at the same rate as the lines 10 are winched in. Another anchor 9 (not shown) is placed at the termination of the array and additional anchors 11, preferably of the type described in copending patent application No. 7791/70 are attached as the array is paid out during the laying operation.

Arrays according to this invention may be used in coastal protection, that is to reduce the effects of erosion and to accumulate sand immediately off shore. The arrays may also conveniently be laid alongside underwater structures such as pipelines or the legs of oil rigs or jettys to prevent damage which may result by the scouring action of water. In general a preferred orientation of an array having the form of loops attached to a base structure is with the planes of the loops transverse to the predominating direction of a current. For coastal protection an array may be set out parallel to a shore or at right angles to it in the fashion of a groyne or a combination of both arrangements may be used depending upon the prevailing conditions.

In an embodiment of this invention an artificial seaweed array for protecting the base of a production platform on a sea bed which is subject to scouring and sand movement is prepared in the following manner. The four sides of a square base structure of 16 meters side comprise four lengths of a cable of the type described in United Kingdom patent No. 1 164842 having a rated breaking load of 7 tons joined together at the four corners. This material is stiff enough to maintain the square shape yet still sufficiently flexible for the array to be rolled or folded. For additional rigidity in this instance two diagonal lengths of the same material are also attached at the four corners. A length of the same type of cable having a breaking load of 1 ton is then attached to opposite sides of the base square in successive runs from side to side so as to produce parallel lengths of the material spanning the square, each separated by a distance of 1 meter. To complete the base structure lengths of braided nylon twine having a breaking load of 0.5 ton are attached to opposite sides of the base square at right angles to the cables of 1 ton breaking load and spaced at 1 meter intervals. The resultant structure is a square network having substantially square meshes of 1 meter side with two diagonal reinforcements. All the intersections of the nylon twine and of the two sizes of cable are lashed together to provide additional-coherence in the base structure.

To form the artificial seaweed array a bundle of continuous polyethylene terephthalate filaments in the form of a 1.5 X l denier tow is attached at 1 meter intervals along the lighter cable a sufficient length being used between adjacent attachments to produce loops having an amplitude of meters. Attaching of the tow to the lighter cable is preferably done before the cable is assembled into the base structure and to facilitate handling of the cable with tow attached the loops of tow between each attachment are drawn together and lightly bound to the cable with a water softened twine such as paper twine which subsequently releases the loops. If desired to further facilitate handling the tow itself may be lightly bound with paper tape also.

A completed array may be wound on a drum for laying as hereinbefore described or prepared for laying by any other suitable means.

What we claim is:

1. An artificial seaweed array comprising of loops of strands arranged in the form of a plurality of loops lying in generally vertical planes, the apexes of the loops being free floating within a body of water and the legs of each loop being horizontally spaced apart but forming a series of interconnecting U-shaped loops with adjacent legs touching each other and attached to a reticular base structure.

2. An array according to claim 1 wherein the loops are self buoyant.

3. An array according to claim 2 wherein the material comprising the loops is selected from the group consisting of polyethylene, polypropylene or a cellular thermoplastic polymer.

4. An array according to claim 1 wherein the loops are denser than the water into which the array is to be laid.

5. An array according to claim 4 wherein the loops comprise strands of a material selected from the group consisting of a polyester or a polyamide.

6. An array according to claim 1 wherein at least part of the reticular base structure is a cable comprising a bundle of substantially parallel filaments encased in a thermoplastic sheath.

7. An array according to claim 1 wherein cross-over points of the base structure are joined.

8. A method for influencing the sedimentation and movement of solid particles of material in seas, lakes and other bodies of water wherein an array of artificial seaweed comprising a plurality of loops of strands arranged in the form ofa plurality of loops lying in generally vertical planes, the apexes of the loops being free floating within a body of water and the legs of each loop being horizontally spaced apart but forming a series of interconnecting U-shaped loops with adjacent legs touching each other and attached to a reticular base structure is placed at the bottom of a body of water and secured by anchoring means.

9. A method according to claim 8 wherein one end of the array wound on a beam or drum mounted on a floating behind a boat or barge is secured to the bottom of a body of water and the array is placed thereon by moving the boat or barge in the required direction and allowing the beam or drum to unwind.

10. An installation for influencing the sedimentation and movement of particles of material in seas, lakes and other bodies of water comprising strand material submerged within the body of water and arranged in the form of a plurality of loops lying in generally vertical planes, the apexes of the loops being free floating within the body of water and the legs of each loop being horizontally spaced apart but forming a series of interconnecting U-shaped loops with adjacent legs touching each other and said loop being directly attached to a reticular structure constructed of ropes or cables; and means for anchoring the reticular structure to the submerged bottom.

II. An installation as in claim 10 wherein each loop is formed of a bundle of strand material the strands of which lie generally parallel to each other.

n: k k 

1. An artificial seaweed array comprising of loops of strands arranged in the form of a plurality of loops lying in generally vertical planes, the apexes of the loops being free floating within a body of water and the legs of each loop being horizontally spaced apart but forming a series of interconnecting U-shaped loops with adjacent legs touching each other and attached to a reticular base structure.
 2. An array according to claim 1 wherein the loops are self buoyant.
 3. An array according to claim 2 wherein the material comprising the loops is selected from the group consisting of polyethylene, polypropylene or a cellular thermoplastic polymer.
 4. An array according to claim 1 wherein the loops are denser than the water into which the array is to be laid.
 5. An array according to claim 4 wherein the loops comprise strands of a material selected from the group consisting of a polyester or a polyamide.
 6. An array according to claim 1 wherein at least part of the reticular base structure is a cable comprising a bundle of substantially parallel filaments encased in a thermoplastic sheath.
 7. An array according to claim 1 wherein cross-over points of the base structure are joined.
 8. A method for influencing the sedimentation and movement of solid particles of material in seas, lakes and other bodies of water wherein an array of artificial seaweed comprising a plurality of loops of strands arranged in the form of a plurality of loops lying in generally vertical planes, the apexes of the loops being free floating within a body of water and the legs of each loop being horizontally spaced apart but forming a series of interconnecting U-shaped loops with adjacent legs touching each other and attached to a reticular base structure is placed at the bottom of a body of water and secured by anchoring means.
 9. A method according to claim 8 wherein one end of the array wound on a beam or drum mounted on a floating behind a boat or barge is secured to the bottom of a body of water and the array is placed thereon by moving the boat or barge in the required direction and allowing the beam or drum to unwind.
 10. An installation for influencing the sedimentation and movement of particles of material in seas, lakes and other bodies of water comprising strand material submerged within the body of water and arranged in the form of a plurality of loops lying in generally vertical planes, the apexes of the loops being free floating within the body of water and the legs of each loop being horizontally spaced apart but forming a series of interconnecting U-shaped loops with adjacent legs touching each other and said loop being directly attached to a reticular structure constructed of ropes or cables; and means for anchoring the reticular structure to the submerged bottom.
 11. An installation as in claim 10 wherein each loop is formed of a bundle of strand material the strands of which lie generally parallel to each other. 